U.S. patent number 5,213,622 [Application Number 07/777,818] was granted by the patent office on 1993-05-25 for cleaning agents for fabricating integrated circuits and a process for using the same.
This patent grant is currently assigned to Air Products and Chemicals, Inc.. Invention is credited to David A. Bohling, John C. Ivankovits, David A. Roberts.
United States Patent |
5,213,622 |
Bohling , et al. |
May 25, 1993 |
Cleaning agents for fabricating integrated circuits and a process
for using the same
Abstract
This invention is a vapor-phase process for cleaning
metal-containing contaminants from the surfaces of integrated
circuits and semiconductors between the numerous fabricating steps
required to manufacture the finished electronic devices. The
process comprises contacting the surface to be cleaned with an
effective amount of a cleaning agent comprising a carboxylic acid
selected from acetic acid or formic acid at a temperature
sufficient to form volatile metal-ligand complexes on the surface
of the substrate to be cleaned. The volatile metal-ligand complexes
are sublimed from the surface of the substrate providing a clean,
substantially residue-free surface.
Inventors: |
Bohling; David A. (Emmaus,
PA), Ivankovits; John C. (Allentown, PA), Roberts; David
A. (Carlsbad, CA) |
Assignee: |
Air Products and Chemicals,
Inc. (Allentown, PA)
|
Family
ID: |
25111377 |
Appl.
No.: |
07/777,818 |
Filed: |
October 11, 1991 |
Current U.S.
Class: |
134/3;
257/E21.226; 510/488; 510/175; 257/E21.225; 257/E21.241;
134/41 |
Current CPC
Class: |
C11D
7/08 (20130101); C23F 1/12 (20130101); H01L
21/02046 (20130101); H01L 21/02085 (20130101); C11D
7/265 (20130101); C11D 7/02 (20130101); C11D
11/0047 (20130101); H01L 21/3105 (20130101); C23G
5/00 (20130101) |
Current International
Class: |
C23G
5/00 (20060101); C11D 7/08 (20060101); C11D
11/00 (20060101); C11D 7/26 (20060101); C11D
7/22 (20060101); C11D 7/02 (20060101); H01L
21/306 (20060101); H01L 21/3105 (20060101); H01L
21/02 (20060101); C23G 001/02 () |
Field of
Search: |
;134/3,41 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4714517 |
December 1987 |
Malladi et al. |
4900363 |
February 1990 |
Brehm et al. |
|
Primary Examiner: Garvin; Patrick P.
Attorney, Agent or Firm: Gourley; Keith D. Simmons; James C.
Marsh; William F.
Claims
We claim:
1. A process for cleaning metal-containing contaminants from a
surface of a substrate of the type used in fabricating integrated
circuits and semiconductors comprising contacting the surface with
an effective amount of a cleaning agent comprising a carboxylic
acid selected from the group consisting of formic acid and acetic
acid in the vapor phase at a temperature sufficient to form a
volatile metal-ligand complex and subliming the metal-ligand
complex to remove the metal contaminants and provide a clean
surface.
2. The process according to claim 1 wherein the substrate to be
cleaned is selected from silicon, silicon oxide,
borophosphosilicate glass, phosphosilicate glass and strontium
titanate.
3. The process according to claim 2 wherein the metal-containing
contaminants to be cleaned from the surface of the substrate
comprise a metal oxide represented by the formulae MO, MO.sub.2,
MO.sub.3, M.sub.2 O and M.sub.2 O.sub.3 wherein M represents the
metal of the metal oxide.
4. The process according to claim 3 wherein the metal-containing
contaminant comprises an oxide of a metal selected from the group
consisting of copper, iron, nickel, chromium and gold.
5. The process according to claim 4 wherein the metal-containing
contaminant comprises an oxide of copper.
6. The process according to claim 2 wherein the metal-containing
contaminant comprises a metal halide represented by the formula
M.sup.+n (X.sup.-).sub.n wherein n is 1, 2 or 3 and X is a
chlorine, bromine or iodine atom.
7. The process according to claim 6 wherein M is selected from the
group consisting of copper, aluminum, nickel, iron, yttrium,
manganese and chromium.
Description
TECHNICAL FIELD
The present invention relates to cleaning agents used in
fabricating semiconductors and integrated circuits and a
substantially residue-free vapor-phase process for using the
cleaning agents. The cleaning agents comprise an effective amount
of a carboxylic acid selected from formic acid or acetic acid.
BACKGROUND OF THE INVENTION
The electronics industry is striving to further miniaturize
semiconductors and integrated circuits while increasing design
complexity. To accomplish that result, the individual active
electrical devices such as transistors, diodes and the like used to
create the circuitry and the interconnects between such devices
must be fabricated on an increasingly small scale. As circuitry
dimensions decrease, contaminants present during the fabrication of
electronic devices cause significantly more device failures and
malfunctions. Therefore, surface contaminants must be carefully
removed to maintain quality standards and to maximize the yield of
fully functioning integrated circuits.
Contaminants present during integrated circuit fabrication include
photoresist materials, residual organic and residual metallic
contaminants such as alkali metals and native/metallic oxides.
Metallic films comprising metal oxides and metal halides are also
inadvertently deposited onto electronic devices during immersion
into etchant or resist stripper baths, both which may contain metal
ions and free metals in solution. Likewise, corrosive chlorides are
deposited on such assemblies contaminants can weaken or embrittle
the electrical connectors of the device as well as delaminate the
layers of the device resulting in current leakages or physical
failure.
Chemical cleaning agents are typically used to remove bonded or
adsorbed metallic oxides and corrosive chloride residues from wafer
surfaces between the numerous individual steps required to
fabricate an integrated circuit. Conventional chemical cleaning is
typically performed using a series of acid and rinse baths. These
cleaning methods are often characterized as "wet" techniques
because the electronic device is immersed in a liquid cleaning
solution immediately prior to performing the next processing step.
Numerous problems are encountered when using liquid cleaning
solutions including incomplete removal of the cleaning agent from
the surface, introducing new contaminants onto the surface to be
cleaned as well as disposing of hazardous liquid wastes.
A typical wet cleaning process for removing film contaminants from
a bare silicon or thermally grown silicon oxide crystal comprises
the steps of:
(1) immersing the wafer in an inorganic resist stripper such as
sulfuric acid/hydrogen peroxide followed by immersing in a sulfuric
acid/oxidant mixture and rinsing with deionized water;
(2) immersing the wafer into a mixture of water/ammonium
hydroxide/hydrogen peroxide to remove metal oxides and metals
followed by rinsing with deionized water;
(3) immersing the still wet wafers into a mixture of
water/hydrochloric acid/hydrogen peroxide to desorb atomic and
ionic contaminants; and
(4) rinsing with distilled water and drying in a inert atmosphere
such as nitrogen. (4) rinsing with distilled water and drying in an
inert atmosphere such as nitrogen.
The above mentioned "wet" cleaning process suffers from numerous
problems: First, ammonia and HCl vapors can mix to form particulate
smoke containing colloidal ammonium chloride particles which can
cause wafer contamination. Special care must also be taken to
prevent depletion of hydrogen peroxide from the cleaning solution
of step (2) because ammonium hydroxide in the absence of hydrogen
peroxide acts as a silicon etchant. Additional contaminants may
also be introduced into the system during the numerous distilled
water rinsing steps required to remove cleaning residue. Finally,
trace moisture must be removed, typically via high temperature
vacuum applications, before conducting the next processing
step.
Disadvantages associated with wet wafer cleaning processes have led
to a search for "dry" cleaning processes wherein the cleaning agent
is applied and removed in the vapor state. In order to conduct a
vapor phase cleaning process, the products formed by contacting the
cleaning agent and the contaminants must possess sufficient
volatility to enable essentially complete removal from the surface
to be cleaned. Manufacturers are continually searching for "dry"
cleaning agents and vapor-phase processes for using such cleaning
agents which eliminate the enumerated problems wherein high quality
electronic devices can be fabricated without using environmentally
harmful reagents.
BRIEF SUMMARY OF THE INVENTION
The present invention is a vapor-phase process for cleaning
metal-containing contaminants from the surfaces of integrated
circuits and semiconductors between the numerous individual
fabricating steps required to form the finished electronic device.
The process for removing metal-containing contaminants residing on
the surfaces of the electronic device comprises contacting the
surface to be cleaned with an effective amount of a cleaning agent
comprising a carboxylic acid selected from formic acid or acetic
acid at a temperature sufficient to form volatile metal-ligand
complexes on the surface of the substrate to be cleaned. The
volatile metal-ligand complexes are then sublimed from the surface
of the substrate to provide a clean, substantially residue-free
surface.
Cleaning agents suitable for practicing this invention comprise one
or a mixture of carboxylic acids selected from the group consisting
of formic acid and acetic acid wherein the cleaning agent and the
metal-containing contaminants are capable of reacting to form a
volatile metal-ligand complex. The subject carboxylic acids have a
sufficiently high vapor pressure under the enumerated operating
conditions to conduct the process in the vapor phase.
In an alternative embodiment, an effective amount of the cleaning
agent is dispersed in an inert atmosphere including but not limited
to nitrogen, argon or helium. In another embodiment, an effective
amount of the cleaning agent is dispersed in an oxidizing
atmosphere wherein the combination of the carboxylic acid and
oxidizing atmosphere is capable of oxidizing the metal-containing
contaminants residing on the surfaces of the substrate to their
corresponding metal oxides, which thereafter, are capable of
reacting with the enumerated cleaning agents to form volatile
metal-ligand complexes. Suitable oxidizing atmospheres include, but
are not limited to, oxygen, an oxygen-containing gaseous mixture,
N.sub.2 O, HCl, HF, F.sub.2, Cl.sub.2 and Br.sub.2.
Metal-containing contaminants can be removed from the surfaces of a
broad range of substrates including silicon, silicon oxide,
borophosphosilicate glass, phosphosilicate glass and strontium
titanate. The process can be utilized to clean any substrate which
is not capable of reacting with the cleaning agents under the
enumerated process conditions. Metal-containing contaminants
capable of being cleaned from the enumerated substrates include
metal oxides represented by the formulae MO, MO.sub.2, MO.sub.3,
M.sub.2 O and M.sub.2 O.sub.3 wherein M represents the metal of the
respective metal oxide. Typical metals include copper, iron,
nickel, chromium and gold. The process is also capable of cleaning
metal-containing contaminants such as metal halides represented by
the formula M.sup.+n (X.sup.-).sub.n wherein n is 1, 2 or 3; X is a
chlorine, bromine or iodine atom and M represents the metal of the
respective metal halide. Representative metals include copper,
aluminum, nickel, iron, yttrium, manganese and chromium.
The invention offers numerous advantages over conventional
wet-cleaning methods because the instant cleaning process can be
conducted in-situ, meaning that the substrate does not have to be
removed from the fabrication apparatus in order to clean
metal-containing contaminants from the surfaces of the electronic
device prior to conducting the next fabricating step. Moreover, the
cleaning agents leave essentially no residue on the surface of the
electronic assembly which might interfere with subsequent
manufacturing steps or assembly performance.
DESCRIPTION OF THE DRAWINGS
The drawing is a graphic depiction of the amount of cleaning
achieved by the instant cleaning process.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a cleaning process for removing
metal-containing contaminants from the surfaces of electronic
devices such as semiconductors and integrated circuits between the
numerous individual fabricating steps required to manufacture the
electronic device. The invention offers numerous advantages over
conventional wet-cleaning processes known in the art. The instant
cleaning process can be conducted in-situ, meaning that the
substrate does not have to be removed from the fabricating
apparatus in order to clean metal-containing contaminants from the
surfaces of the substrate prior to conducting the next fabricating
step. Moreover, Applicants' cleaning agents leave essentially no
residue on the surfaces of the substrate which might interfere with
subsequent manufacturing steps.
The process for removing metal-containing contaminants residing on
the surfaces of the electronic device comprises contacting the
surface to be cleaned with an effective amount of a cleaning agent
comprising a carboxylic acid selected from formic acid or acetic
acid at a temperature sufficient to form volatile metal-ligan
complexes on the surface of the substrate to be cleaned.
The term, effective amount, as applied to the cleaning agents of
this invention, refers to that amount of the subject carboxylic
acids required to obtain the desired cleaning activity. The
effective amount of cleaning agent required to practice the claimed
process is easily determined by those familiar with the art and
will depend upon the manner in which the cleaning agent is
delivered into the fabricating apparatus. Typical pressures
generated by the ligands at temperatures between about 100.degree.
and 400.degree. C. range from 10 torr to about 760 torr although
the operating pressure is not critical to the practice of the
invention.
In an alternate embodiment, an effective amount of the cleaning
agent is dispersed in an inert atmosphere. Suitable inert
atmospheres include nitrogen, argon and helium. The optimum amount
will vary depending upon the particular cleaning ligand used, the
metal-containing contaminants to be cleaned from the surface and
the surface loading of the contaminant. Typical gas phase ligand
concentrations range from 1.0% to about 100.0%, and preferably,
from 5.0% to 25.0% of the desired ligand dispersed in the desired
inert atmosphere.
In another embodiment, an effective amount of the cleaning agent is
dispersed in an oxidizing atmosphere wherein the combination of the
carboxylic acid cleaning agent and oxidizing atmosphere is capable
of oxidizing the metal-containing contaminants residing on the
substrate's surfaces to their corresponding metal oxides. Typical
gas phase ligand concentrations range from 1.0% to about 100.0%,
and preferably, from 5.0% to 25.0% of the desired ligand dispersed
in the desired oxidizing atmosphere. The resulting metal oxides are
capable of reacting with the enumerated cleaning agents to form
volatile metal-ligand complexes. Suitable oxidizing atmospheres
include, but are not limited to, oxygen, an oxygen-containing
gaseous mixture, N.sub.2 O, HCl, HF, F.sub.2, Cl.sub.2 and
Br.sub.2. An example of an oxygen-containing gaseous mixture is
zero-grade air (a gaseous mixture containing about 19.5 to 23.5 mol
percent oxygen and less than 0.5 mmole percent hydrocarbon, with
the remainder comprising nitrogen, sold by Air Products and
Chemicals, Inc., Allentown, PA).
The term, metal-ligand complexes, refers to the reaction product of
the metal-containing contaminant and the cleaning agent formed
in-situ during the process. The volatile metal-ligand complexes
residing on the surfaces of the electronic device or substrate are
then sublimed from the surface providing a clean, substantially
residue-free surface. The process substantially reduces the amount
of metal-containing contaminants residing on the substrate's
surfaces which can interfere with the depositing of conducting
metals, etching steps and masking operations required to
manufacture electronic devices.
The cleaning agents according to the present invention can be
applied by both machine and manual operations known in the art. The
particular cleaning agent to be utilized and the appropriate method
for delivering the cleaning agents to the substrates to be cleaned
will depend upon numerous factors including the properties of the
electronic device, the type of metal-containing contaminants to be
removed from the substrate's surface and the like. The term,
cleaning agent refers to an effective amount of formic acid, acetic
acid, or a mixture thereof.
Applicants' process is capable of removing metal-containing
contaminants from a broad range of substrates used in manufacturing
electronic devices such as integrated circuits and semiconductors.
Any substrate having metallic-containing surface contaminants
wherein the substrate is not capable of reacting with the
enumerated cleaning agents under the specified process operating
conditions can be used in the present process. Representative
substrates include, but are not limited to silicon, silicon oxide,
borophosphosilicate glass, phosphosilicate glass and strontium
titanate.
The instant cleaning process utilizing the cleaning agents
disclosed herein can be used to remove numerous metal-containing
contaminants. For purposes of interpreting the claims, the
invention contemplates any metal-containing contaminant which is
capable of reacting with the cleaning agents of the present
invention to form volatile metal-ligand complexes. Representative
metal-containing contaminants include metal oxides represented by
the formula MO, MO.sub.2, MO.sub.3, M.sub.2 O and M.sub.2 O.sub.3
wherein M represents the metal of the respective metal oxide. While
M may represent a broad range of metals, representative metals
include copper, iron, nickel, chromium and gold. The process is
also capable of cleaning metal-containing contaminants such as
metal halides represented by the formula M.sup.+n (X.sup.-).sub.n
wherein n is 1, 2 or 3; X is a chlorine, bromine or iodine atom and
M represents the metal of the respective metal halide. Again, M
represents a broad range of metals including copper, aluminum,
nickel, iron, yttrium, manganese and chromium.
While the instant process is particularly suited toward cleaning
metallic films residing on the surfaces of electronic devices, the
process can also be used for selectively cleaning one metallic film
while maintaining the integrity of another metallic film residing
on the substrate's surface. The selective process can be employed
whenever two or more discrete metal-containing contaminants such as
metal oxide films or metal halide films are present on the surface
of a device wherein the reaction of the cleaning agent with a
particular metal-containing contaminant occurs more rapidly than
with the other contaminant residing of the substrate's surface.
The particular cleaning agent to be utilized and the appropriate
method for delivering the cleaning agents to the surfaces to be
cleaned of metal-containing contaminants depends upon numerous
factors including the amount of metallic film to be cleansed,
sensitivity of the electronic components to the cleaning agent, the
desired time allotted for the cleaning process, the surface loading
of the contaminant and the like.
In order to more fully describe the practice of the present
process, a general embodiment of the cleaning process will now be
presented. The substrate to be cleaned is placed in a heated
chamber, such as a chemical vapor deposition chamber, commercial
chemical vapor deposition furnace tube or commercial cleaning tool
used in elevated temperature processes. The substrate can also be
left in the original process chamber, such as a plasma etching
reactor, provided that the chamber can be brought to the
appropriate cleaning process temperature. The substrate is then
heated to the desired temperature, typically from about 100.degree.
to 400.degree. C. The desired cleaning agent is delivered to the
electronic device to be cleaned by heating the cleaning agent to a
temperature sufficient to create a sufficient operating vapor
pressure. Alternately, the carboxylic acid may be dispersed in the
desired oxidizing atmosphere or inert atmosphere and passed into
the hot zone of the selected apparatus by conventional
techniques.
The cleaning agent may be continuously or intermittently delivered
into the reactor or cleaning chamber. The process can also be
conducted in one or more stages. For example, the metal-containing
contaminants may be initially oxidized by subjecting the device to
be cleaned to an enumerated oxidizing atmosphere followed by
treating the device with the desired cleaning agent at a later
time. Alternately, the process may be conducted in one stage
wherein the cleaning agent reacts with metal-containing
contaminants such as metal oxides and metal halides residing on the
substrate's surface to form volatile metal-ligand complexes which
are then conveniently sublimed from the surface to provide a
substrate which is substantially residue free.
Metals in the zero oxidation state residing on the surface of the
substrate may also be oxidized by reacting the metal with the
carboxylic acid cleaning agent or the oxidizing atmosphere at
elevated temperature to produce the corresponding metal oxides
which then further react with additional cleaning agent to form the
volatile metal-ligand complex. These volatile metal-ligand
complexes are conveniently sublimed from the surfaces of the device
to produce a cleaned surface. The cleaning pattern can be
conveniently controlled by masking operations known in the art
wherein portions of the metallic surface which are not to be
cleaned are covered with a material which will not react with the
cleaning agent.
The cleaning agents of the present invention have been shown to
react with metallic films comprising the oxides of copper, iron,
nickel and chromium which typically reside on electronic devices
during fabrication. The resulting metal-ligand complexes are
sufficiently volatile such that following sublimation, essentially
no residue remains on the substrate. Sublimation can also be
assisted by pulling a partial or full vacuum on the device.
The above-mentioned embodiment represents a significant advance in
gas-phase cleaning processes. This gas-phase cleaning process
offers numerous advantages over conventional wet cleaning processes
in that the above-mentioned ligands easily saturate an oxidizing or
inert atmosphere and react exclusively with the metal oxides and
metal halides of interest without the aid of a catalyst to form
reaction products which are sufficiently volatile to leave
essentially no residue on the surface of the device.
The instant cleaning process can be practiced at temperatures
comensurate with those used in conventional cleaning processes.
Typical temperatures for practicing the process range from about
100.degree. to 400.degree. C. The optimum reaction time and
temperature for practicing the process will vary depending upon the
particular ligand used, the type and quantity of metal-containing
contaminant to be cleaned and the like. Typical processing time
ranges from about 5 to 50 minutes depending upon contaminant
loading of the surface.
The following example is provided to further illustrate an
embodiment of the present invention and is not intended to restrict
the scope of the invention. In the following example, temperatures
are set forth uncorrected in degrees Celsius.
EXAMPLE
CLEANING OF METAL-CONTAINING CONTAMINANTS FROM A SILICON SURFACE
USING A CLEANING AGENT COMPRISING FORMIC ACID
Bare <100> silicon wafers (6 sq. in.) with native oxide were
doped with metallic contaminants by standard evaporative techniques
and were analyzed by Rutherford backscattering to determine the
level of trace contaminants comprising copper, gold, indium and
chloride anion. Each wafer was scored and segmented into
approximately one square inch regions. The wafers were placed at a
30 degree angle in a glass boat. Filtered zero grade air was
bubbled through formic acid at a rate of 83 sccm or 4.1% formic
acid in the process stream. The formic acid was delivered to a
glass tube heated to 200.degree. C., and the wafers were exposed to
the cleaning agent for about 40 minutes. The results are shown in
the FIGURE wherein the amount of cleaning achieved by the instant
cleaning process is graphically depicted. The results are presented
in numerical form in the Table. Rutherford Backscattering analysis
provides a detection limit of about 0.5.times.10.sup.-13 atoms/sq.
cm.
TABLE ______________________________________ CLEANING OF SILICON
SUBSTRATE WITH FORMIC ACID CLEANING AGENT Fe Au Cu In Cl
______________________________________ Initial Level 0.862 0.88
0.43 0.058 0.215 Final Level 0.946 0.478 0.054 0.058 0.22
______________________________________
The results according to the FIGURE and Table demonstrate that at
200.degree. C. the cleaning agent comprising formic acid
effectively removed substantially all of the copper contaminants
from the surface while removing about 55% of the gold-containing
contaminants. In contrast, essentially no iron-, indium- or
chloride-containing contaminants were removed at the specified
reaction temperature. Further experiments indicate that higher
temperatures must be utilized to effect removal of gold-, indium-
and chloride-containing contaminants from the surfaces of the
enumerated substrates. Thus, a selective process for removing one
metal-containing contaminant from another can be achieved by merely
controlling the process temperature and pressure of the cleaning
agent.
The present vapor-phase cleaning process for removing
metal-containing contaminants from the surfaces of electronic
devices during their fabrication offers numerous advantages over
typical wet cleaning methods known in the art because the instant
cleaning process can be conducted in the vapor-phase utilizing
thereby eliminating the necessity for exposing the substrate to the
clean room environment during apparatus transfer. Recontamination
via exposure to other contaminants is thereby avoided. Moreover,
the cleaning agents leave essentially no residue on the surface of
the electronic assembly which might later interfere with subsequent
manufacturing steps.
Having thus described the present invention, what is now deemed
appropriate for Letters Patent is set out in the following appended
claims.
* * * * *